It has recently been determined that the human pathogen, Neisseriae gonorrhoeae, produces an extracellular enzyme which cleaves only human IgA as substrate. More specifically, human IgA of the IgA1 is susceptible, IgA2 being resistant. Because mucosal antibody, seemingly responsible for defence against gonorrhoeae is predominantly of IgA isotope, the IgA protease enzyme may allow the microorganism to circumvent humoral antibody attack. Accordingly, we are attempting to determine what ratio of subclasses of IgA is produced by normal human mucus membranes, using in vitro organ culture of gastrointestinal mucosa. Secondly, we are studying the binding of gonocci to human cells in tissue culture to determine if the organism releases IgA proteases when bound, and to what extent this interferes with anti-gonoccal secretory IgA added to prevent binding.